This invention relates to a field emission cathode and a method for manufacturing the same, and more particularly to a field emission cathode used as an electron source for a display unit, an image-pickup unit, a high-frequency device or the like and a method for manufacturing the same.
When an electric field of a level as high as about 109 (V/m) is applied to a surface of a metal material or that of a semiconductor material, a tunnel effect occurs to permit electrons to pass through a barrier, resulting in the electrons being discharged to a vacuum atmosphere even at a normal temperature. Such a phenomenon is referred to as xe2x80x9cfield emissionxe2x80x9d and a cathode constructed so as to emit electrons based on such a principle is referred to as xe2x80x9cfield emission cathodexe2x80x9d.
One of conventional field emission cathodes which have been known in the art is of the Spindt type, which includes emitters each formed of metal such as molybdenum (Mo) or the like into a chip of a cone-like shape, as well as gate electrodes. An electric field of a low level is applied between the gate electrodes in proximity to the emitters to permit the emitters to emit electrons. Unfortunately, the field emission cathode of the Spindt type requires to deposit a high-melting metal material such as Mo or the like by electron beam (EB) deposition and bore holes in the gate electrodes (lead-out electrodes) and an insulating layer, to thereby cause an increase in manufacturing cost of the field emission cathode, resulting in mass-production of the field emission cathode increased in size being rendered difficult.
It is known in the art that diamond-like carbon emits electrons in an electric field of a low level. There is known a field emission cathode utilizing such a phenomenon, which uses a photoresist material modified. More particularly, the photoresist material is formed with projections by means of a transfer mold and then heated, resulting in being modified. This permits the thus-modified photoresist material to be increased in carbon-carbon covalent bond, to thereby exhibit electrical conductivity. The carbon-carbon bond has diamond-like carbon which is increased in crystallization mixedly contained therein.
However, the transfer mold is made of a silicon wafer, resulting in being limited to a size of up to 12 inches. Also, the transfer mold is removed from the modified photoresist layer by etching, resulting in being restricted to only one-time use. Further, the conventional process or method using diamond-like carbon for the emitters fails to readily form the lead-out electrodes while keeping them in proximity to the emitters. Absence of the lead-out electrodes fails to permit an advantage of the diamond-like carbon such as low-voltage drive to be satisfactorily exhibited.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a field emission cathode which is capable of emitting electrons under a reduced voltage.
It is another object of the present invention to provide a method for manufacturing a field emission cathode which is capable of providing a field emission cathode attaining the above-described object.
In accordance with one aspect of the present invention, a field emission cathode is provided. The field emission cathode includes an insulating layer, lead-out electrodes formed on the insulating layer, openings formed at a lamination between the insulating layer and each of the lead-out electrodes, emitters each arranged in each of the openings, a cathode electrode, and a modified photoresist layer arranged on a lower surface of the insulating layer and modified by heating. The cathode electrode is electrically connected to the photoresist layer. The photoresist layer has projections exposed from the insulating layer. The emitters each are constituted by a distal end of each of the projections of the photoresist layer.
In a preferred embodiment of the present invention, the field emission cathode further includes a resistive layer so arranged that the cathode electrode is electrically connected through the resistive layer to the modified photoresist layer.
In accordance with another aspect of the present invention, a method for manufacturing a field emission cathode is provided. The method includes the steps of forming a cathode electrode pattern on a cathode substrate, forming a photoresist layer, superposing an intaglio provided with recesses for formation of projections and coated thereon with a release agent on the photoresist layer, subjecting the photoresist layer to molding under a pressure while being heated, to thereby form the photoresist layer with the projections and modify the photoresist layer, peeling off the intaglio, subjecting a surface of the modified photoresist layer to etching, forming an insulating layer on the modified photoresist layer, forming a gate electrode pattern on the insulating layer, and subjecting a lamination between lead-out electrodes on the gate electrode pattern and the insulating layer, to thereby form the lamination with openings, wherein the projections of the photoresist layer each are exposed at a distal end thereof from a portion of the insulating layer positioned at each of the openings.
In a preferred embodiment of the present invention, the method further includes the step of forming a resistive layer pattern on the cathode electrode pattern, followed by formation of the photoresist layer pattern.
In accordance with this aspect of the present invention, method for manufacturing a field emission cathode is provided. The method includes the steps of forming a cathode electrode pattern on a cathode substrate, forming a photoresist layer on an intaglio formed with recesses for formation of projections and coated thereon with a release agent, superposing the cathode layer and intaglio on each other in a manner to render the cathode electrode pattern and photoresist layer opposite to each other, forming a photoresist layer, superposing an intaglio provided with recesses for formation of projections and coated thereon with a release agent on the photoresist layer, subjecting the photoresist layer to molding under a pressure while being heated, to thereby form the photoresist layer with the projections and modify the photoresist layer, peeling off the intaglio, subjecting a surface of the modified photoresist layer to etching, forming an insulating layer on the modified photoresist layer, forming a gate electrode pattern on the insulating layer, and subjecting a lamination between lead-out electrodes on the gate electrode pattern and the insulating layer, to thereby form the lamination with openings, wherein the projections of the photoresist layer each are exposed at a distal end thereof from a portion of the insulating layer positioned at each of the openings.
In a preferred embodiment of the present invention, the method further includes the steps of a resistive layer pattern on the cathode electrode pattern and superposing the cathode substrate and intaglio on each other in a manner to render the resistive layer pattern and photoresist layer opposite to each other. Such construction effectively prevents flowing an overcurrent and concentration of a current to any specific emitters.
Thus, the method of the present invention permits the field emission cathode capable of emitting electrons by merely applying a voltage of a low level between the lead-out electrodes and the projections to be readily manufactured at a reduced cost.